It sounds like you're doing pretty good. He should be sleeping more, but I don't know if that would effect his weight, the book Healthy Sleep Habits; Happy Child can help with the sleep.
I know the bottle gives a sense of security because you can see him drinking it, but babies are way better at getting the milk out than pumps so try giving it to him straight for a bit. If you want to know how many ozs, you can rent a scale like they use at the drs office and weigh him before and after feedings. The fattiest part of your milk is the hind milk, it comes in the second half of the feeding, so try nursing on one side only per feeding, let him stay on that side as long as he wants and the breast seems way empty. Also make sure you are getting enough fat in your diet, if your not getting any, then neither is he. 2% or whole milk, full-fat yogurt, cheese, make sure you're getting enough. No offense to drs, but a lactation consultant or LLL will be more help than your ped. Go ahead and try all that, but remember that percentages are just statistics and averages, and he is a baby. If he seems happy and is smiling and holding his head up on schedule and his length and overall weight keeps increasing, some kids are just skinny. Don't worry about it too much.